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Oviposition Preference and Development of Rice Weevil, Sitophilus Oryzae (lin.) (coleoptera: Curculionidae) in Different Stored Grains

Masuma Akhter
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Shanjida Sultana
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Tangin Akter
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Shefali Begum
Department of Zoology, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

Oviposition preference and development of rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae) were observed in three varieties of stored grains i.e. parboiled rice (Oryza sativa), wheat (Triticum aestivum) and pulse (Cicer arietinum). In no choice tests, the mean number of eggs laid were 360.3 2.60 in rice, 382 2.49 in wheat and 394 2.06 in pulse. In case of choice tests, the mean number of eggs laid were 13.6 (+-) 0.4 in rice, 14.2 (+-) 0.37 in wheat and 15.6 (+-) 0.4 in pulse. The differences between the number of eggs laid in rice, wheat and pulse varied significantly in both no-choice and choice tests. The respective incubation period, larval and pupal period of the weevil reared on rice, wheat and pulse were 5.7 (+-) 0.27, 5 (+-) 0.47 and 5.4 (+-) 0.27 days, respectively, 21 (+-) 0.47, 20.3 (+-) 0.27, 19 (+-) 0.47 days, respectively and 10.3 (+-) 0.27, 10.7 (+-) 0.27, 11.3 (+-) 0.27 days, respectively. The total development time from egg to adult recorded in rice, wheat and pulse was 37 (+-) 0.47, 36 (+-) 0.47 and 35.6 (+-) 0.72 days, respectively. The difference between the larval periods was significant (p < 0.05) when they reared in wheat and pulse. The larval and pupal period varied significantly (p < 0.05) between the individuals reared in rice and pulse. The developmental period was shorter in pulse than in rice and wheat.

Keywords: Oviposition, Preference, Development, Rice weevil, Stored grains

Location: Department of Zoology, University of Dhaka.

Start Date: 00-00-2013

End Date: 00-00-2014

Program Area: Pest Management

Commodity: Insects

Objectives:

The present study was conducted to gain information on oviposition preference and development of rice weevil that will be of great value towards the process to protect grains in a better way and to derive all its advantage.

Methodology:

Studies on the life cycle and oviposition preference of Sitophilus oryzae (L.) on three different stored grains rice, pulse and wheat were conducted during 2013-14 in the Entomology laboratory, Department of Zoology, University of Dhaka. This investigation was carried out within an incubator set at temperature 27 (+-) 4⁰C and 70 (+-) 4% relative humidity (rh). These temperature and rh were selected because they were reported to be most favorable conditions for population growth of weevil. Rice weevil was collected from the stored rice of Shamsun Nahar Hall Dining Mess, University of Dhaka. The weevils were identified. The weevils were sexed under the microscope by means of their rostrum characteristics and abdomen deflection. Three different types of grains i.e. parboiled rice (Oryza sativa), pulse (Cicer arietinum) and wheat (Triticum aestivum) were collected from local grain stores of Dhaka city. Any cracked or damaged grains were removed. Any extraneous materials, if found were also removed to get only fresh grains as test samples. All grains were sterilized at –18⁰C for two weeks in a freezer. After the treatment, the grains were spread on normal white papers at room temperature 28(+-) 4⁰C and 70(+-) 4% rh for 24 hours to bring them to normal temperature and kept in sealed containers before they were used. Stock culture of the rice weevil, Sitophilus oryzae was maintained in an incubator at 27 (+-) 4⁰C and 70 (+-) 4% rh to ensure their regular supply for tests throughout the experimental period. The mass rearing medium was parboiled rice. Stock cultures were maintained in five large Petri dishes (10" diameter). Each Petri dish was filled with approximately equal quantities (300 g) of rice grains. Fifty pairs of adult rice weevils were released into each of five Petri dishes for oviposition. A wet cotton ball was kept regularly within the Petri dishes to maintain the moisture. After 48 hours of oviposition, the adult weevils were completely sieved out from each Petri dish using a 1.5 mm sieve. The metabolic wastes and intervals cleared regularly to avoid grain dampness and microbial growth. Experiments were started to conduct with the insects emerged from the second generation of the rearing S. oryzae and so on. For no choice test, 100 grains (not cracked or broken) from each type (Rice, Pulse, Wheat) were kept in separate Petri dishes (5" diameter). Five pairs of newly emerged adults of age group 24 - 48 hrs were released in each Petri dish. The Petri dishes were kept in incubator at 27 ± 4⁰C and 70 ± 4% rh. Released insects were allowed to oviposit for three days. Similar test was continued for five times using the same insects. After each test the grains were collected and the grains containing eggs were separated out by examining with magnifying glass and the number of eggs laid were counted. The experiment was replicated five times. For choice test, 50 grains (not cracked or broken) from each type (Rice, Pulse, Wheat) were kept together in one Petri dish (5" diameter). Five pairs of newly emerged adults of age group 24 - 48 hrs were released in the Petri dish. The Petri dish were kept in incubator at 27 ± 4⁰C and 70 ± 4% rh. Released insects were allowed to oviposit for three days. After three days, the grains were collected and the grains containing eggs were separated out by examining with magnifying glass and the number of eggs laid were counted. The experiment was replicated five times. To study the life cycle of rice weevil Sitophilus oryzae (L.) 100 grains (not cracked or broken) from each different type of grains (Rice, Wheat and Pulse) were kept in Petri dishes. Ten pairs (male and female) of newly emerged adults of age group 24 - 48 hrs were released in each Petri dish. There were five such replications for each variety that were marked as Rep.-1, Rep.-2 and Rep.-3 and so on. The Petri dishes were kept in incubator at temperature 27 + 4⁰C and 70 ± 4% rh. Weevils were kept for two days to oviposit. Damaged grains were replaced regularly with uninfested grains. Grains containing eggs were separated out by examining under microscope and were used for further study. The grains (rice, wheat, pulse) on which the rice weevils laid eggs were transferred into another sets of Petri dishes (3" diameter). To determine the incubation period 10 grains were dissected with a pair of forceps under the microscope from the day of oviposition to egg hatching. Thus, incubation period was recorded. The remaining seeds were used for the determination of larval- and pupal period. On hatching the larvae of rice weevil were allowed to feed individually inside the grains in Petri dish. Five grains per day were dissected with a pair of forceps to see the larval period. The dissection of grains was continued until they attained the pupal stage. The period between egg hatching and pupation was observed as larval period. Within the infested grains when the larvae attained the pupal stage the seeds were allowed as such until adult emergence. The period between formations of pupae till the adult emergence was noted as pupal period. Standard deviation, standard error and t test were calculated. For evaluating relative effectiveness of life cycle and oviposition of rice weevil on different type of grains, the experimental data were subjected to ANOVA.

Source of Information: Bangladesh J. Zool. 45(2): 131-138, 2017 ISSN: 0304-9027 (print) 2408-8455 (online)

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Achievement/Findings:

From the present study, it may be concluded that the rice weevil, Sitophilus oryzae preferred pulse more to oviposit than rice and wheat. Oviposition increased with the increase of the adult age. The development of Sitophilus oryzae was quicker in pulse than in rice and wheat.

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